1. Field of the Invention
This invention relates to a zoom lens, and in particular, to a zoom lens which is small in size, high in image quality, and low in cost, used in a camera having an electronic imaging means, such as a camcorder or a digital camera.
2. Description of Related Art
A conventional zoom lens which has a variable magnification ratio of approximately 3 and offers a compact design and low cost for civilian use is set forth in Japanese Patent Preliminary Publication No. Hei 11-258507.
This zoom lens includes, in order from the object side, a first lens unit with positive refracting power, fixed when the magnification of the zoom lens is changed; a second lens unit with negative refracting power, moved from the object side toward the image side in the range of a wide-angle position to a telephoto position when the magnification is changed; a third lens unit with positive refracting power, moved from the image side toward the object side in the range of the wide-angle position to the telephoto position when the magnification is changed; and a fourth lens unit with positive refracting power, moved when the magnification is changed. In this case, a variable magnification function is shared between the second lens unit and the third lens unit, and thereby compactness of the zoom lens is achieved.
Zoom lenses set forth in Japanese Patent Preliminary Publication Nos. Hei 8-320434, Hei 8-271787, and Hei 4-43311 are known as zoom lenses with variable magnification ratios of 6-10 in which the third lens unit is fixed when the magnification is changed.
A zoom lens with a variable magnification ratio of about 20 is disclosed in Japanese Patent Preliminary Publication No. Hei 8-82743 in which the movement of the third lens unit of the zoom lens is complicated.
A high density of pixels of an electronic image sensor has recently been achieved, and a high image quality, not to speak of a compact design and low cost, is required for an imaging optical system. Increases in contrast and resolution fall within the category of this high density of pixels, and thus it is necessary to give special consideration to chromatic aberration and the entire photographing range. It is also necessary to ensure the amount of marginal light and to improve the F-number of a lens accordingly.
However, it is not said that the above conventional zoom lenses bring about image qualities corresponding to electronic image sensors in which the number of pixels is over two millions and a pixel pitch is below 3.8 xcexcm. Alternatively, it is not said that a cost reduction is achieved, taking account of compactness and productivity.
It is, therefor an object of the present invention to provide a zoom lens which is capable of obtaining an image quality corresponding to an electronic image sensor having a great number of pixels or small pixels, compactness, and low cost at the same time.
In order to achieve this object, the zoom lens according to the present invention includes, in order from the object side, a first lens unit with positive refracting power, a second lens unit with negative refracting power, a third lens unit with positive refracting power, and a fourth lens unit with positive refracting power. At least, the second lens unit and the fourth liens unit are moved along the optical axis to change spaces between individual lens units, and thereby the magnification of the zoom lens is changed in the range of the wide angle position to the telephoto position. In this case, the third lens unit has three positive lens elements and one negative lens element located at the most image-side position.
In the zoom lens according to the present invention, it is desirable that the above first lens unit is constructed with a positive lens component.
The zoom lens according to the present invention includes, in order from the object side, a first lens unit with positive refracting power, a second lens unit with negative refracting power, a third lens unit with positive refracting power, and a fourth lens unit with positive refracting power. At least, the second lens unit and the fourth lens unit are moved along the optical axis to change spaces between individual lens units, and thereby the magnification of the zoom lens is changed in the range of the wide-angle position to the telephoto position. In this case, the fourth lens unit consists of, in order from the object side, a cemented lens component with positive refracting power and a single lens component with positive refracting power.
In the zoom lens according to the present invention, it is desirable that the above first lens unit is constructed with a positive lens component.
This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.